Gelled aqueous acidic composition containing an in situ crosslinked reaction product



United States Patent ABSTRACT OF THE DISCLOSURE Aqueous acidic compositions gelled with a polymer having pendent amide or nitrile functions crosslinked by a monomer containing a plurality of {-CH OR) groups.

bonded to amido nitrogen and a process for their preparation. The gelling system of this invention finds particular utility in explosive compositions based on an oxidizing agent and one or more fuels or sensitizers.

BACKGROUND OF THE INVENTION The handling of liquid acidic compositions has long been a complicating factor in their use in various industries such as oil production, propellants, metallurgy, fertilizers and explosives, due to the inherent corrosiveness and, in some cases, strong oxidizing capacity of the acids. In more recent years, there has been increased interest in developing means of safely handling acidic compositions. This interest has been particularly evident in the explosives industry particularly with respect to compositions containing an inorganic oxidizing agent together with sensitizer or fuel components since the discovery of the greater work potential of water-bearing compositions containing these constituents. Since the constituents of such explosive compositions exhibit varying degrees of solubility, difficulty was encountered in maintaining the homogeneity of aqueous explosive compositions of this type. The use of such compositions for blasting in Wet boreholes was still further complicated by the seepage of water into the explosive compositions, altering the constitution of the composition by dilution and leaching of the soluble components.

To help solve these problems, various thickeners or gelling agents have been used with slurried explosive compositions based on inorganic oxidizing salts. Satisfactory thickener systems for these compositions are based on natural hydroxylated polymers such as natural polysaccharides, particularly galactomannan gums and their derivatives.

The versatility of these systems is increased by the provision of various crosslinking agents which gel the compositions thereby increasing the stability of the system and usually imparting other beneficial effects. Some variations in product consistency is possible by varying the proportions of hydroxylated polymers and crosslinking monomers in the compositions, but usually water-resistance is seriously deficient at concentrations low enough to provide readily pourable compositions. In particular there is a now well-recognized need for a gelling system for aqueous compositions which will provide stable, pourable compositions which exhibit good water resistance as Well as being of use in forming the more conventional firm, highly viscous gels.

While the gelling systems of the prior art provide satisfactory performance for most aqueous compositions based on inorganic oxidizing salts which are to be of relatively high viscosity, renewed interest in explosives based on nitric acid, i.e., compositions sometimes referred to as Sprengel explosives, has presented new problems since the known thickening and gelling systems are not satisfactory in the strong acid. For example, explosives based on concentrated nitric acid as the primary oxidizing component exhibit exceptionally high acidity and oxiding capacity which are particularly hazardous in fluid compositions. Further, the use of these compositions in wet conditions is accompanied by generation of high temperatures due to dilution of nitric acid with water. Gelling systems of the types used in compositions based on inorganic oxidizing salts tend to decompose under acidic conditions. In addition, these gelling systems in general require careful control of pH during formation, which control i not possible in the nitric acid based compositions, and are not operable in a highly acidic medium. Thickening of the nitric acid based compositions, e.g., by inorganic fillers or linear polymers, does not provide stable, cohesive, water resistant compositions having premium explosive properties.

SUMMARY OF THE INVENTION Accordingly, there is still a need for aqueous acidic compositions having a gelling system which can be used in a wide range of acidic compositions to give stable, water-resistant cohesive products ranging from pourable, yet water-resistant fluids to rigid gels. The instant invention provides compositions of improved homogeneity water-resistance and stability which help meet this need.

The instant invention provides an improvement in gelled aqueous acidic compositions, the improvement comprising a gelling system comprising the in situ crosslinked reaction product of at least one polymer containing a plurality of pendent groups selected from amide and nitrile functions, the amide nitrogen atoms bearing at least one hydrogen, and at least one monomer containing a plurality of CH OR groups bonded to amido nitrogen, wherein R is selected from hydrogen and lower alkyl of up to 4 carbon atoms. Preferably the polymer comprises about from 0.1 to 10% by weight of the acidic composition and the monomer comprises about from 0.5 to 50% by weight of the polymer. While the instant invention is useful for gelling various acidic compositions such as nitric acid, to facilitate their handling and use, it finds particular utility when used in conjunction with acidic explosive compositions comprising one or more fuels and an oxidizing component. This invention further provides a process for the manufacture of these gelled compositions which comprises bringing into contact, in an aqueous composition having a pH of less than about 6.0, at least one polymer containing a plurality of pendent substituent groups selected from amide and nitrile functions, the amide nitrogen atoms bearing at least one hydrogen, and at least one monomer containing a plurality of CH OR groups bonded to amido nitrogen, wherein R is as defined above.

DESCRIPTION OF PREFERRED EMBODIMENTS The gelling system of this invention can be used with a Wide range of acids including the common mineral acids such as nitric acid, perchloric acid, sulfuric acid, hydrochloric acid, and phosphoric acid and Water soluble or miscible organic carboxylic acids having a dissociation constant in Water of at least about l 1 0 such as lower aliphatic monocarboxylic acids. These can include, for example, formic, acetic, propionic, butyric or iso'butyric acid, lower aliphatic diand polycarboxylic acids of 2 to 7 carbon atoms such as oxalic acid, malonic acid, succinic acid, and glutaric acid. The pH of the acidic compositions is less than about 6.0 and preferably less than about 5.5. Of the above-named acids, the mineral acids and salts derived therefrom whose aqueous solutions are acidic, e.g., ammonium nitrate, are particularly well suited for forming the gelled structures of this invention. In gelling organic acids, the presence of small quantities of a mineral acid can be desirable to speed gelation. Aqueous nitric acid and aqueous solutions of ammonium nitrate are particularly preferred acidic compositions to be gelled in accordance with this invention since, as will be described and exemplified more fully hereinafter, there is a particular utility for these interalia in the formulation of explosive compositions. Nitric acid of about from to 99% strength can be used; but nitric acids having concentrations of greater than 50% are most often used, and concentrations of about from 65 to 98% are particularly preferred.

In addition to its usefulness in gelling substances which are considered as acids per se, the gelling system of this invention also finds utility with aqueous acidic solutions of compatible substances. Examples of such substances include: ammonium nitrate, ammonium perchlorate, ammonium chlorate, ammonium sulfate, ammonium bisulfate, and ammonium phosphate and solutions or suspensions of other compositions, e.g., sugar, which have been made acidic.

In this specification the term lower alkyl means an alkyl radical of from 1 to four carbon atoms, unless otherwise indicated.

Polymers which can be used in accordance with this invention include, for example,

(1) Polymers of which at least about 2% of the units are wherein X is selected from H CN and %N and the Rs can be the same or different and each is independently selected from the group consisting of hydrogen, lower alkyl, hydroxyalkyl, or cyanoalkyl radicals having up to 4 carbon atoms, and

(2) A polymer containing recurring units of the forwherein R is as defined above.

Examples of such polymers which are especially suitable for use in accordance with this invention from the viewpoint of solubility and dispersi-bility in the liquid phase of the acidic compositions and availability at reasonable cost include poly(acrylic amides) which are polymers of acrylamide or methacrylamide, polymers of N-substituted derivatives of acrylic acides such as N-methylacrylamide, N-ethylacrylamide, and N-methylmethacrylamide, and polymers of hydroxyalkyl derivatives of amides such as a,2-hydroxyethyl acrylamide and a-hydroxymethacrylamide. Examples of poly(acrylic nitriles) which can be used in this invention include polymers of acrylonitrile, methacrylonitrile, a-butylacrylonitrile, and a-hydroxymethacrylonitrile. In general, homopolymers of the above-mentioned acrylic amides or nitriles or their mutual copolymers are preferred polymers because of their low cost and ease of dissolution in a wide range of acidic liquids. Particularly preferred polymers are homopolymers of acrylamide and of acrylonitrile and copolymers of acrylamide and acrylonitrile in ratios varying about from 1/20 to 20/1. Copolymers comprising at least about 2% of amide or nitrile units as defined above and the balance over copolymerized units can also be used.

Representative copolymerizable monomers include acrylic monomers, e.g., acids such as acrylic acid, methacrylic acid, u-ethyl acrylic acid and u-propyl acrylic acid; esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl methacrylate and n-hexyl acrylate; cycloalkyl substituted acrylics, e.g., cyclohexyl methacrylate; salts such as sodium or ammonium acrylate or alkyl ammonium acrylates; hydroxyalkyl acrylates, e.g., 2-hydroxyethyl acrylate or 2-hydroxypropyl acrylate; cyanoalkyl acrylics such as a-cyanoethylacrylonitrile; nonacrylic monomers such as sodium styrene sulfonate, vinyl acetate, vinyl pyridine and vinyl pyrrolidone and mixtures of "two or more of such monomers, providing the copolymer formed meets the solubility and stability requirements set forth. Although low concentrations of monomers having pendent amide or nitrile functions in the copolymers can sometimes be used, e.g., as low as 1 to 2%, these monomers usually will comprise at least about 2% of the copolymer. Preferred polymers include vinyl addition polymers soluble in the system used herein, preferably having a molecular Weight of about from 50,000 to six million. Crosslinking monomers which can be used in accordance with this invention can be selected from any compound having a plurality of -(CH OR) groups bonded to amido nitrogen. Each CH OR group can be bonded to a separate nitrogen atom, forming a plurality of =NCH OR groups, or, alternatively, two CH OR groups can be attached to a single nitrogen atom. Such monomers include, for example, poly(hydroxymethyl)ureas such as N,N -bis(hydroxymethyl) urea, i.e., dimethylolurea; N,N' bis(alkoxymethyl)ureas such as N,N'-bis(methoxymethyl)urea and N,N'-bis(ethoxymethyl)urea; poly(hydroxymethyl)aliphatic amides such as methylene bis( N hydroxymethylformamide), N,N bis(hydroxymethyl)adipamide, N,N bis-(hydroxymethyl)sebacamide, N,NN" tris(hydroxymethyl) melamine, hexakis(hydroxymethyl)melamine, bis(hydroxymethyl)forrnamide, N,N bis(hydroxymethyl) acrylamide; N,N-(alkoxymethyl)aliphatic diamides such as N,N'-bis (methoxymethyl)sebacamide; N,N substituted dinitramines such as N,N'-bis(hydroxymethyl)hexamethylene dinitramine; N,N'-substituted sulfamides such as N,N bis(hydroxymethyl)N,N dimethyl sulfamide and N,N'-bis(methoxyrnethyl)N,N'-dimethyl sulfamide; and N,N-substituted disulfonamides such as N,N'-bis(hydroxymethyl) 1,6 bis(methylsulfonamido)hexane, and mixtures of two or more of the above.

Of the above illustrative crosslinking monomers, N,N- bis(hydroxymethyl)urea is especially preferred for the compositions of the instant invention.

The term soluble in the aqueous acidic component and similar terms as used herein, refer to components having appreciable solubility at ambient temperatures, i.e., about 20 to 25 C., in the particular aqueous, acidic component to be gelled. In general, this solubility should be at least about 10% by weight and preferably appreciably greater, e.g., 50% or more. The reaction between acrylic polymer and crosslinking monomer should not preferentially form products which separate, e.g., by precipitation, from the aqueous acidic composition or agglomerate into fiocculates or lumps. Crosslinking of the polymer chains forms a structure which is a gel rather than a precipitate. This gelled structure swells in and holds the aqueous, acidic composition and is of substantially constant composition throughout. The gelled crosslinked structure contains a relatively low ratio of polymer solids to liquid phase, e.g., less than about 1 to 10, this ratio being roughly equal to the Weight ratio of combined polymer and monomet to the liquid phase, in contrast to precipitates or agglomerates in which there is a high ratio of polymer solids to liquid phase.

The gelled compositions of this invention are stable. That is, there is little or no degradation of the polymer, crosslinking monomer or their reaction products in the aqueous acidic composition to be gelled. Since prolonged stability is particularly desirable, stability refers particularly to absence of degradation of a crosslinked system when subjected to accelerated thermal stability tests which involve heating the sample at a temperature of 50 C. (122 F.) for a period of at least 8 to 12 hours.

Strength, when used herein with regard to acids, particularly to nitric acid, expresses in percent the relationship between the weight of 100% (dry) acid and the weight of acid plus water in the particular acid.

The polymer for the gelling system preferably is provided as preformed polymer. However, if desired, the polymer can be formed in situ in the acidic liquid in the presence of free-radical polymerization initiators which are soluble to the extent of at least about 0.1% in the acidic liquid. Suitable initiators include sodium, potassium and ammonium salts of inorganic peracids; hydrogen peroxide; and organic peroxide and azo catalysts. Generally, persulfates are preferred. The persulfate ions, which are introduced as a soluble persulfate salt, can be used alone in the solution of inorganic oxidizing salt to promote the polymerization reaction or an added reducing agent can also be employed to form a redox couple.

Formation of firm gel compositions can be completed in reasonably short times, e.g., less than about 30 minutes, at temperatures of about 20 to 25 C., particularly in strong oxidizing acids such as nitric acid. Rapid gelling is facilitated by using polymers, of relatively high molecular weight, i.e., of one up to 6 million or higher for polyacrylamide.

Preformed polyacrylamides which can be used in this invention include Cyanomer P-250, commercially available from American Cyanamide and Polyhall 295M commercially available from Stein Hall. Particularly preferred polyacrylonitriles are Orlons, commercially available from Du Font and those prepared by emulsion polymerization techniques according to Sorenson and Campbell, Preparative Methods of Polymer Chemistry, p. 169. Preferred copolymers consist of 2 to 25% acrylamide and 98 to 75% acrylonitrile prepared by emulsion polymerization in accordance with Encyclopedia of Polymer Science and Technology, vol. I, p. 400; these copolymers have intrinsic viscosities in 0.1% solutions in dimethylformamide at 30 C. of 8.0 to 10.0. As will be exemplified below, gels of very desirable properties can be formed from lower molecular weight polymers but higher molecular weight polymers form gels more rapidly at lower temperatures and, in addition, usually require the use of less crosslinking monomer to provide gels of equivalent properties, other ingredients and conditions remaining the same.

The amide monomers employed for in situ polymerization in the explosive compositions of this invention need not be highly purified. For example, crude acrylamide sulfate obtained by the hydrolysis of the corresponding nitrile, acrylonitrile, in the presence of concentrated mineral acid, e.g., sulfuric acid, can be used directly without purification. The presence of the minor residual amounts of mineral acid in the crude monomer catalyzes the crosslinking reaction making possible faster gel times and exerts no detrimental effect in the explosive composition. Additional acid, such as sulfuric acid, can be added in amounts of about from 0.5-5% as a positive catalyst to hasten gelling of the aqueous phase of the compositions.

The amount of polymer used in the gelling system will generally vary from about 0.1 to by weight of the liquid acidic composition and preferably about from 0.5 to 5% by weight. About from 0.5 to 50% of the crosslinking monomer based on the weight of the acrylic polymer will usually be employed.

Preparation of the gelled compositions of this invention can be accomplished by simply incorporating the polymer (preformed or formed in situ) and crosslinking monomer into the liquid acidic medium. There is no need for any catalyst and reaction between the polymer and crosslinking monomer in most cases begins shortly (within seconds) after addition of the polymer and monomer. Usually the polymer is admixed with the acidic composition and the crosslinking monomer subsequently added to the composition.

In general, gels form more rapidly when heat, e.g., of about from 30 to C., is applied than when the reaction is carried out at or near ambient room temperature. However, when the acidic composition is also a strong oxidizer and particularly when it is nitric acid, heating to temperatures above about 50 C. preferably should be avoided. In the preparation of blasting compositions based on aqueous solutions of inorganic nitrate it is particularly convenient to use concentrated aqueous solutions of ammonium nitrate commonly known in the art as ammonium nitrate liquor, the aqueous liquid phase of the composition being provided for the most partby this solution. In forming the gelled compositions of this invention care should be taken that all ingredients, viz,the polymer, crosslinking monomer and, if desired, any ,solid to be dispersed in the gel, are uniformly dispersed through the composition. Agitation used for blending and dispersing of components is desirably continued until the composition is gelled, particularly when particulate solids for example, fuels or sensitizers such as trinitrotoluene, smokeless powder and/or aluminum used in explosive compositions, are to be distributed uniformly through the gel matrix. In some instances, for example, in explosive compositions which are to contain a high percentage of solid trinitrotoluene or when a solid which inhibits polymerization or the crosslinking reaction is to be incorporated in the compositions, all ingredients except such additives can be mixed and gelled and such additives blended into the gel formed.

When the polymer is to be formed in situ, the rate of polymerization and, in some instances, product consistency can be adversely affected by the presence of nitrogen oxides and oxygen, either in dissolved form or as the gases, and by the presence of large amounts of compounds conventionally used to inhibit free-radical polymerizations of the monomers. Compensations for these variations can be provided, when necessary, by increasing the concentrations of polymerization pro moters. An alternative and generally more economical expedient, however, is to reduce the concentrations of these polymerization-retarding components prior to the polymerization. In the case of nitrogen oxides and oxygen, this can be accomplished by carrying the polymerization out under a blanket of an inert gas, typically nitrogen. To further eliminate polymerization inhibiting concentrations of nitrogen oxides and/or oxygen, the components of the blasting composition, particularly the aqueous solution of inorganic oxidizing salt, can be sparged with the inert gas. When preformed in polymer is used, as is preferred, there is no need to sparge the components.

The rate of gelling and the viscosity of the gelled compositions of this invention can be varied according to the needs of a particular application. In general, the rate-of gelling and the viscosity of the gel can be increased by increasing the percentage of polymer in tho system, by increasing the relative proportion of cross linking monomer used for a given quantity of the polymer. by increasing the molecular weight of the polymer employed in the system, or any combination of the above.

The gelled compositions based on an inorganic oxidizer can be employed for a variety of applications in which liquid aqueous acidic compositions are ordinarily employed, as an acidifying agent in mineralogical and other processes, in preparing salts, and in like operations. The gelled nitric acid compositions find particular merit as an oxidizing or nitrating acid in chemical synthesis in such applications when delayed action is desirable or required; inasmuch as the gels tend to release the acid slowly.

Several of the gelled acidic compositions based on nitric acid or an oxidizing salt are inherently satisfactory as detonating explosives Without further additives, i.e., they can be detonated with moderate-strength primers in diameters of 6 inches or less under moderate conditions of confinement, such as provided by a borehole or a container of moderate wall thickness. However, for explosive applications, the compositions of this invention also preferably contain one or more fuels and/or sensitizers which are stable in the acid of the strength used in preparing the gels. Examples of non-explosive fuels are the monoand dinitro aromatic hydrocarbons, such as nitrobenzene, o-mononitrotoluene and dinitrotoluene; liquid and solid hydrocarbons and hydrocarbon fractions, particularly refined petroleum and mineral oils and the aromatic hydrocarbons, such as benzene, toluene, and the xylenes; carbohydrates, including various cellulose and starch products, e.g., cornstarch, potato starch, wood and paper pulps and sugar; siliceous fuels, including silicon itself and mixtures and alloys of silicon with heavy metals, e.g., ferrosilicon; and sulfurous fuels such as sulfur itself and pyrites. Metal fuels such as aluminum or ferrophosphorus are also useful in some of the gelled compositions, provided that they are, or can be made, sufficiently resistant to attack by the nitric acid. The gel copolymer per se acts as a fuel and except as otherwise indicated is included in calculating the amount of nonexplosive fuel and oxygen balance. Ordinarily, the gells for use as explosive compositions will be formulated to have an oxygen balance of about from 25 to +10%.

In addition to the non-explosive fuels and/or sensitizers named above the explosive compositions of this invention can, in some embodiments, contain one or more additives of the art-recognized self-explosive type, provided that such additive is stable in the strengths of acidic composition used in preparing the gels. Trinitrotoluene, for example, exhibits a high degree of stability in all strengths of aqueous nitric acid and ammonium nitrate liquors and hence is a particularly useful additive of the self-explosive" type. Examples of other selfexplosive components which can be used in the compositions of this invention are RDX, HMX, tetryl, PETN, nitro-cellulose, smokeless powder, and other organic nitramines, nitrates and nitrocompounds. For reasons of economy and compatibility, trinitrotoluene is the preferred self-explosive for use in the compositions of this invention. The trinitrotoluene or mixtures thereof (e.g., with ammonium or sodium nitrate) can be intro duced into the compositions in the form of crystals, grains, pellets, flakes, or other particulate form which allows ready dispersion thereof. In general, up to 85%, and preferably up to 40%, by weight of self-explosive additive based on weight of the composition can be used.

Stable, gelled nitric acid compositions found especially economical and eflicient as detonating explosives comprise a uniform blend of:

(a) About from 25 to 95% by weight of aqueous nitric acid having a strength of about from 50 to 99%, and preferably 65 to 98%.

(b) About from to 30% of a non-explosive fuel, preferably selected from siliceous fuels, light metals, liquid and solid hydrocarbons, carbohydrates, sulfur, monoand dinitro aromatic hydrocarbons, and mixtures of such fuels and/ or sensitizers;

(c) Up to about 40% of a self-explosive sensitizer, particularly trinitrotoluene;

(d) Up to about 50% of an inorganic oxidizing salt, typically an inorganic nitrate; and

(e) An in situ copolymerization product of (1) About from 0.1 to and preferably 0.2 to 5%, based on the Weight of aqueous nitric acid of at least one polymer as defined above, which preferably is formed from acrylamide, acrylonitrile, methacrylonitrile, or methacrylamide or is a copolymer of monoethylenically unsaturated monomers of this group, and

(2) About from 0.5 to 50% and preferably 0.1 to 10% by weight based on component (1) of a crosslinking monomer as defined above, and preferably N,N'-bis (hydroxymethyl urea.

Particularly preferred explosive compositions based on inorganic oxidizing salts and having an oxygen balance of about from 25 to +10% comprise:

(a) About from 20 to 70% ammonium nitrate;

(b) Up to 40% and preferably 10 to 25% sodium nitrate;

(0) Up to 40% and preferably 10 to 30% self explosive;

(d) Up to 30% of metallic fuel, preferably 2 to 20% of aluminum and/or 5 to 25% of ferrophosphorus;

(e) Up to 10% of non-explosive fuel, preferably selectedfrom carbonaceous, siliceous or sulfurous fuels or combinations thereof;

(f) From 5 to 45% and preferably 10 to 30% of water;

(g) An in situ formed product of (1) About from 0.1 to 10% and preferably 0.2 to 5% based on the aqueous phase of the composition of at least one polymer as defined above, and preferably a poly (acrylic amide) and (2) About from 0.5 to 50% based on the weight of the polymer (1) of a crosslinking monomer as defined above, which monomer is preferably N,N-bis(hydroxymethyl)urea.

In general, the gelled blasting compositions of this invention are prepared by blending of the ingredients, e.g., in a rotary type mixer such as a Lightnin AG-l00 mixer, keeping in mind the same general considerations for the control of the process as were discussed above. As mentioned, it is generally preferred to use preformed polymer to avoid the need for sparging and for maintaining the components while being blended under an inert gas atmosphere until polymerization is complete. Usually, the nitric acid is introduced into the mixing vessel first and the other ingredients added individually thereto While the contents of the vessel are being agitated. The crosslinking monomer is usually the last ingredient added. Agitation is usually continued until after the composition'is gelled, particularly when the added fuels or sensitizers are solids such as for example, ferrosilicon, sulfur, aluminum, silicon, or starch, which must be distributed uniformly throughout the gel matrix. Where fuels or other additives of marginal stability or additives which inhibit polymerization are to be incorporated in the compositions, all ingredients except such additives can be mixed and gelled as previously described, then such additives blended with the finished gel.

As indicated above, for explosive applications preferred ranges of nitric acid strength are about from 60% (corresponding to a maximum water content of about 40%) to 97%. In general, the unit or bulk strength of an explosive composition based on gelled nitric acid increases with increasing strength of the nitric acid gelled. Accordingly gels of nitric acid of strength or higher are usually employed where high bulk strength is a requisite, e.g., in the bottom of a borehole. The bulk or unit strength of an explosive composition, its relative ease of initiation, and its minimum critical diameter can also be regulated to a large degree by the type and quantity of fuel and/or sensitizer employed. Organic nitro compounds, typically mononitrotoluene, or dinitrotoluene, or in particular a self-explosive composition, especially trinitrotoluene, are incorporated to provide compositions which are easily initiated, e.g., by a relatively small primer or by a blasting cap, in some cases, in small diameters. In many cases, a combination of fuels will be employed within the range of proportions indicated to give a composition having the desired physical and explosive properties.

Preferred gelling systems for explosive compositions comprise polymers of acrylonitrile, acrylamide, methacrylonitrile or methacrylamide, or copolymers thereof. The crosslinking monomer preferred is N,N-bis(hydroxyethyl)urea. In addition to being readily available at reasonable cost, these compositions are particularly effective in providing firm cohesive gels having viscosities within the desired range of 100,000 to million cps., high surface tension as evidenced by lack of stickiness or tackiness, ready workability, flexibility, water resistance, and other desirable physical characteristics in the asmade state. Further compositions including these preferred gelling systems retain their initial physical and explosive properties during storage after production. The preferred gelling systems also allow relatively wide latitude in the consistency of the explosive product made to fit the needs of a particular type of blasting.

This invention therefore provides simple and effective modified aqueous acidic compositions which are easier and safer to handle than those known heretofore and which have controlled free acidity and excellent stability. These and other properties of the gelled acidic compositions of this invention make the products of this invention particularly suitable as propellants, cleaning solutions, oil well treating agents, and etching compositions, in chemical syntheses, as an acidifying agent in mineralogical processes, in fertilizers, and in other uses where aqueous acid is now employed. In addition, physical properties such as cohesiveness, controlled flexibility and consistency and the ability to maintain dispersion of solids therein as well as their explosive properties make In the following examples which illustrate this invention, parts, percentages and ratios are by weight unless otherwise indicated. In the following examples, the terms noted below mean the following:

Very firmViscosity of about from 3 million to 10 million cps. as measured with TR 1 spindle at 0.5 r.p.m. on the Brookfield Synchro-lectric viscometer.

Firm-Viscosity of about from 1 million to 3 million cps. measured with a TE spindle at 1.0 r.p.m. on a Brookfield Synchro-lectric viscometer, Model RVT, with helipath attachment.

Medium firm--Viscosity of about from 400,000 to 1 million cps. using the same conditions of measurement on the viscometer.

Weak-Viscosities generally less than about 400,000 cps. generally 200,000 to 400,000 cps.

Examples 1-34 Gelled nitric acid compositions of this invention are prepared from the materials noted in Table 1. The polymer is first disclosed and admixed in nitric acid of the strength indicated and the crosslinking monomer. is then added with agitation, which is continued until gelation is substantially complete. The reaction temperature is as noted in the table. Gelation time refers to the interval of time between the addition of the last ingredient and the first appearance of gelled product. None of the gel products show visible signs of deterioration at ambient temperatures (ca. 20-25 C.) over periods of 1 week, the

(methylsulionamido)hexane, 6.6%.

I notnotes at end of table.

compositions of this invention, 'particularly those conmaximum periods of observation. taining conventional fuels and sensitizers, readily adaptai to formulanon.m fixefl plant faclhtles as Wen as 1 Changes in spindle and r.p.m. necessary to obtain accurate bile and other on-site equipment. readings,

TABLE 1 E Q P l t 0 ll ki re m; of Temp s i'en 0 er ercen ross n n monomer pe e Example per nii of $30 p polymer g Additives 0: Gel product description and gel time 1 70 P01 ac larnlde 1 1.2 N N-bis h di'oxymethynm'eii 6.67 55 Medium gel in sec. 70 ".3102 N:N-bishgdroxymethyDureai 1 6 /31. Medium firm gel in 2 min. 70 do. N, '-bis ydroxymethyhurea, 3 3 25 F rm gel in 45 m n. 70 Polyacrylamide, 3% N,N'-bis(hydroxymethyburea, 13%- 25 F rm gel in 48 min. 70 liolyacrylamide, 2%..- bis01ydroxymethyl) urea, 10% 55 F rm gel n 140 sec. 80 do. bis(hydroxymethyl)urea, 4% 50 Firm gel in 27 sec. 70 Polyaci'ylamide, 1 N,N-bis(hydroxymethy1)urea, .75% 50 weaizgeilili 9 mm.;; firm to medium 0. ge in rs. 8 70 P01 ac lamlde, 1.27 N N-bls(hydroxymethyl) urea 6.6'7 25 Weak gel in 25 min.; firm gel overnight. 9 80 ""2102 n N,N-bis(hydroxymethyl)urea; .3% 35 lvieldium gel overnight (thickened ca. r. 10 do. ..do 35 Weak gel in 12 min..; medium gel in 14 min. 11 do. ..do N55150:, 35 Medium gel in 15 min.

12 70 Polyacrylemide, 2%-... N,N-bis(hydr0xymethyl) 55 Gel in 47 sec. (expanded later).

adipamide, 20%.

70 Polyaerylamlde, 1.6%... Nldii bisgliiydroymethyl) 55 Medium firm gel in 104 see.

a pam e 70 IEolyacrylamlde, 2%..- N,Ni,N-tris(hg droxymetliyl) 50 Highly blown, yellow gel in 10 min.

me amine l0 70 Polyaerylamlde, 1.6%.-. N,Nl,Ni;tris5(l2)3;droxymethy1) 25 Week gel in 1 hr.

me am e 70 .do. hexakiseiyd'mxyiilethyi) 50 Firm gel in 2 mm; highly expand d melamine, 12.5%. y gas. 70 Polyaerylamide, 1.2%... N,N-bis(hydroxymethyl) 50 Weak gel in 8 min.

sebacamide, 13.3%. 70 -.do. N,N'-bis(methoxymethyl)urea, 3.3% 50 Medium gel in 90 sec. 95 Polyacrylamide 0.6%- N,N'-bis(hyd.roxymethyl)u.rea, 8.3% 25 Weak gel in 3 hrs.; medium gel in 3 days. Polyaerylonitrile, 1%. N,N'-bis(hydroxymethyDurea, 5%. 50 Medium firm gel 111:3 min. 75 do. N,N-bis liydroxyinethyl)urea, 10% 45 Medium firm gel in 6 min.; became firmer on standing. 95 Polyaeryloriitrile, N,N-bis(hydroxymethyburea, 18.3% 25 Medium firm gel in 26 min.

0.75 Polyae i ylonitrile, 4%... N,N-bls(hydroxymethyl)urea, 1 50 Cheese-like gel in min. 80 Polyacrylonitrile 4%... N ,N'-bis(hydroxymethyl) urea, 10% 50 Medium firm gel H1 13 min.

70 Copolymer oi acryl- Bis(hydroxymethyl)urea, 1.6% 35 Medium firm gel in 3 min.; firm gel in onltrile and acryl- 5 min.

amide, 1.2. 70 Copolymei' of acryl- Bis(hydroxymethyl)urea, 5.3% 25 Week gel in 12 min.

onitrile and acrylemidefi 0.75%. 27 75 Copolynier of acryl- N,NJois(hydroxymethyDurea, 6.6% 25 Medium firm gel in 20 hrs.

ariiiige anldzaycryhni r e 28 75 Copolyn'ier oi s icryldo 35 Medium firm gel in 45 mm.

amide and acrylonitrilefl", 1.2%.

29 70 Polyiierylamide, 1 2%.-. N,N-bis(hydroxy nethyl) 35 Week gel in 2 hrs.

hexamethylenedinitramine, 10%. 30 70 .do. ..d0 50 Weak gel in 7.5 min. 31 70 do. N,N-bis(hydroxymethyl)-1,6-bis 45 Medium gel in 5 min.

TABLE l con tinued Aq. HNO;

strength, Polymer, percent Crosslinking monomer, percent of Temp.,

Example percent of HNO; polymer Additives 0. Gel product description and gel time 32 70 ..-..do. N,N-bis(hydroxymethyl)-1,6-bis 45 Weak gel in 5 min.

(methylsuionsmido) hexane, 3.3%

33 70 .-...do.1 N,N-bis(hydroxymethyi) 25 Medium firm gel in 1% hr., firm overiormamide, 6.6%. night.

34 70 .-do. ..d 50 Firm gel within 25 min.

Cyanomer P-250-Polyacrylamide available commercialllly from American Cyanamid 00.; molecular weight, -6 ml 1011.

2 Acrylamide polymerized in situ in the nitric acid at C. using initiator system of 0.14% ammonium persulfate, 0.04% CUSO4'5H2O and 0.008% NsHr-HzO; molecular weight, ca. to 1 million.

3 Cyanomer P26Low molecular weight copolymer of aclamide and acrylic acid available from American Cyanamid 4 Polyhall 295M--Polyacrylamide, commercially available from Stein-Hall Corp., contains about 12% acrylic acid in the form of sodium salt; molecular weight, 5-6 million.

5 High molecular weight polyacrylonitrile prepared by emulsion polymerization as by Sorenson and Campbell, Preparative Methods of Polymer Chemistry, p. 169; molecular weight 1.5 million; nnm=17.0 in DMF at Explosive compositions are provided from the compositions in Examples 1-34 by incorporating in the gelled composition a fuel, particularly a carbonaceous fuel or a monoor dinitro-substituted aromatic compound, to give an oxygen balance of about from -10% to 0%.

Examples -43 "Lovv molecular weight copolymer prepared by emulsion polymerization comprising 20% acrylamide and 80% acrylonitrile; prepared by method described in reference cited for footnote 8.

Copolymer comprising 12.5% acrylamide and 87.5%

acrylonitrile, prepared by method as described in reference cited for footnotes 8 and 9, above.

To aqueous ammonium nitrate solution at 65 C. are added sodium nitrate and monomeric acrylamide. Mixing is begun and continued about three minutes to assure uniform dispersion of ingredients. A aqueous solution of ammonium persulfate is then added to initiate polymerization of acrylamide in situ. After about ten minutes pellets of trinitrotoluene are blended into the composition until complete incorporation and dispersion thereof are observed. N,N' bis(hydroxymethy1)urea is then added as a cross-linking agent for the polyacrylamide. Gel formation is observed in about 5 minutes after this addition. The firm, gelled compositions are transferred into 5-inch diameter polyethylene bags (25 lbs./ bag). When detonation of the composition is initiated, in air, by two conventional primers, each comprising 1 lb. (454 g.) of cast trinitrotoluene, the compositions detonate completely at the velocities shown.

TABLE 2 Additives Polymer, Crosslinking monomer, percent of aq. Temp., Gel product description and Example percent of aq. NHlNOa percent of polymer NH4NO 0 gal time N,N-bis(hydroxymethyDurea, 6.6% Medium firm gel in 15 sec. N,N'-b s(hydroxymethyburea, 3.3%.. 60 Weak gel in 90 sec. N,N'-b1s(hydroxymethyhurea, 6.6%.- 30 Medium firm gel in 25,6 min. N,N-bis(hydroxymethyDurea, 2.7%.. NaNO 25% 60 Firm gel in 13 sec. N,N-bis(hydroxymethyburea, 3.1 NaNOa, 17% 45 Medium firm gel in 5 sec. N,N-bis(hydroxymethyDurea, 1%... 45 Firm gel in 3 min. N,N-bis (hydroxymethyburea, 0.5%-- 45 Medium firm gel in 3 min.

N,N-bis(rnethoxymethyl)urea, 6.6%. 50 Firm gel in 1 min. o-. 25 Finn gel in 6 min.

Examples 44-45 Gelled explosive compositions based on ammonium nitrate and of the formulation shown below are prepared as follows using a gelling system wherein polyacrylamide is formed in situ and subsequently crosslinked.

Trinitrotoluene 19. 26 39. 06 N,N-bis (hydroxymethyDurea--. 0. 34 0. 20 Detonation velocity, m./sec 2,380 5, 400

' Catalyst to assure acidity.

Examples 46-47 Firm, gelled explosive formulations based on nitric acid as the oxidizing agent are prepared of the formulations shown below. Each composition is gelled by the 2 The combining of ingredients and particularly the in-situ formation of polymer are conducted under a blanket of nitrogen.

in situ reaction of polyacrylamide (commercially available as Cyanomer P-250) with N,N'-bis(hydroxy- 14 droxymethyl)urea in situ basically as described in Examples 1-34.

TABLE 4 N,N-bis (hydrxymethyl) urea, Polyacrylpercent of amide, polyacryl- Temp., I Example Acid percent amide C. Additives Results 54 37% HCl 2.0 35 Firm gel instantly.

2.0 10 25 o. 56 60% acetic acid 2.0 10 45 E 504, 1.6% Thickening in 10 min; firm gel overnlght.

methyl)urea. Various fuels and sensitizers as shown are Example 57 incorporated in the formulations by first thoroughly blending all compositions except the N,N-bis(hydroxymethyl)urea in the aqueous nitric acid, then adding this ingredient and finally continuing mixing for about 10 to minutes, during which time the reaction runs substantially to completion.

The gelled formulations are loaded into S-inch-diameter cartridges (20 lbs/cartridge) and tested unconfined at 32 F. In each case, detonation of the charge is effected by a primer comprising 1 lb. (454 g.) of cast trinitrotoluene.

Example 48 An explosive formulation of the composition summarized below is prepared basically as described in Examples 46-47. This composition, which forms a firm gel, is transferred into 2% inch diameter containers (200 g./container) and tested by actuating by a 50 g. RDX pellet.

75% HNO 85.1 Starch 2.5 Mineral oil 11.1 Copolymer of 75/25 acrylonitrile/acrylamide 1.2 N,N bis(hydroxymethyl)urea 0.1

Detonation velocity, m./sec. ca 5000 Examples 49-53 Explosive compositions as shown in Table 3 are prepared as described in Examples 46-47 using an aromatic nitro compound as a soluble sensitizer-fuel and copolymers of acrylamide and acrylonitrile as the polymer. D indicates the composition detonates when actuated by a conventional primer comprising 1 pound of trinitrotoluene.

TABLE 3 Example 49 50 51 52 53 75% HNO; 78. 0 78. 0 78. 0 72.0 78. 0 Copolymer:

Acrylic terpolymer 3. 0

25775 acrylamide/acrylonitrile- 10/90 acrylamide/acrylonitrile- 1 0 5(95 acrylamide/acrlonitrile 1.2 N itrobenzene 20. 8 20. 8 20. 8 21. 0 Dinitrotoluene, 26 25. 0 N ,N -bis(hydroxymethyburem- 0. 05 O. 05 0. 05 0. 05 0. 1 Gelling temperature, F--. 70 70 70 70 70 Gel time (hrs) 1% 2% 1% 1% 4 Detonation results". D D D D D Terpolymer consisting essentially of 93.7% polyacrylonitrlle, 6% methyl acrylate. and 0.3% sodium styrene sulionate.

Examples 54-56 Acids indicated in Table 4 are gelled by the reaction of polyacrylamide (Cyanomer P-250) and N,N'-bis(hy A copolymer of methyl vinyl ether and maleic anhydride (commercially available as Gantrez AN) is reacted with aqueous ammonia to give a polymer of the structure This polymer is dissolved in nitric acid, the amount of polymer being 8% by weight of the acid. To this solution at 50 C. is then added 2.5% (based on the weight of the polymer) of N,N-bis(hydroxymethiyl)urea. A weak gel forms in 10 minutes.

I claim:

1. In gelled aqueous acidic explosive compositions comprising a fuel and an inorganic oxidizing component, the improvement which comprises providing a gelling system comprising the in situ crosslinked reaction product of (A) at least one polymer containing a plurality of pendent groups selected from amide and nitrile functions, the amide nitrogen atoms bearing at least one hydrogen, and

(B) at least one monomer containing a plurality of CH OR groups bonded to amide nitrogen, wherein R is selected from hydrogen and a lower alkyl of up to 4 carbon atoms.

2. A composition of claim 1 wherein the oxidizing component is nitric acid having a strength of about from 50 to 99% and comprises about from 25-95% by weight of the gelled composition.

3. A composition of claim 2 wherein the fuel is carbonaceous.

4. A composition of claim 2 wherein the fuel is a hydrocarbon of up to about 20 carbon atoms.

5. A composition of claim 2 wherein the fuel is an aromatic nitrocompound.

6. A composition of claim 2 wherein the fuel is trinitrotoluene.

7. A composition of claim 2 wherein the polymer is polyacrylonitrile and comprises about from 0.1 to 10% by weight of the total gelled composition, and the crosslinking monomer is N,N'-bis(hydroxymethyl)urea and comprises about from 0.5 to 50% by weight of the polymer.

8. A composition of claim 1 wherein the oxidizing component is an inorganic oxidizing salt.

9. A composition of claim 8 wherein the inorganic oxidizing salt comprises, by weight of the acidic composition, about from 20-70% ammonium nitrate and up to 40% of sodium nitrate.

10. A composition of claim 9 wherein the fuel comprises trinitrotoluene.

11. A composition of claim 9 wherein the fuel comprises a carbonaceous combustible.

12. A composition of claim 9 wherein the polymer is polyacrylamide and comprises about from 0.1 to 10% by weight of the total gelled composition, and the crosslinking monomer is N,N-bis(hydroxymethyl)urea and comprises about from 05-50% by weight of the polymer.

13. A process for gelling aqueous acidic explosive compositions comprising a fuel and an inorganic oxidizing component which comprises bringing into contact, in an aqueous composition having a pH of less than 6,

(A) at least one polymer containing a plurality of pendent substituent groups selected from amide and nitrile functions, amide nitrogen atoms hearing at least one hydrogen, and

(B) at least one monomer containing a plurality of CH OR groups bonded to nitrogen wherein R is selected from hydrogen and lower alkyl of up to 4 carbon atoms.

14. A process of claim 13 wherein the polymer is preformed and is admixed with the aqueous composition prior to the addition of the monomer thereto.

15. A process of claim 13 wherein the polymer is formed in situ by forming an aqueous solution of at least solution of at least one acrylic monomer of the general formula wherein X is selected from 16 and the Rs are independently selected from the group consisting of hydrogen, lower alkyl, hydroxyalkyl or eyanoalkyl radicals having up to 4 carbon atoms, and polymerizing the acrylic monomer composition in the presence of at least one free radical initiator.

References Cited UNITED STATES PATENTS 3,164,503 1/1965 Gehrig 149.74 X 3,242,019 3/1966 Gehrig 14974 X 3,282,754 11/1966 Gehrig 149- 74 3,296,044 1/ 1967 Gehrig 149-74 X 3,306,789 2/1967 Logan et a1. 149,74;X 3,336,981 8/1967 Barron et a1. 149, 74, X 3,361,601 1/1968 Chrisp 149- 19 3,376,176 4/1968 Gehrig 149-46 3,423,257 1/1969 Simpson et al 149-74 X 3,423,258 1/1969 Cross 149-19 3,442,728 5/1969 Simpson et a1 149--74,.X 3,444,014 5/1969 Chrisp 149-74 X 3,447,979 6/ 1969 Bluhm et al 14974 X BENJAMIN R. PADGETI, Primary Examiner S. J. LECHERT, JR., Assistant Examiner US. Cl. X.R. 

